PP23A-1068
Magnetic Susceptibility Record Of Loess-Paleosol Sequence In Yili Basin, Central Asia
In recent years, loess-paleosol sequences have been received significant attention for their detailed records of local and regional climatic and environmental changes superimposed on a global signal(Oches and Banerjee, 1996). Magnetic susceptibility, regarded as a simple, rapid and low-cost method, is a very useful proxy to characterize both terrestrial and ocean climatic changes and lithostratigraphic correlation. In some loess- paleosol sequences, including those of the Chinese Loess Plateau, Tajikistan and the Czech Republic, maxima in magnetic susceptibility values correspond with the paleosol horizons, and minima with the least-weathered loess layers. In other loess-paleosol sequences, including those of Siberia, Alaska and Argentina, the relationship is completely opposite, with susceptibility minima associated with the most developed paleosols (Maher et al, 1998). Here, we present the results of magnetic susceptibility of loess-paleosol sequences since the last interglacial period in Yili basin, North Xinjing, central Asia. We selected two loess-paleosol sections at different altitudes in Yining basin surrounded by Tianshan, Central Asia. Talede (TLD) section (N43.34, E83.02) is located the fourth terrace at 850 m altitude with 350mm annual precipitation and annual temperature 8¡æ. Kurdenengbula(KD) section (N43.46, E83.92) is located at 1400 m altitude with 550mm annual precipitation and annual temperature 5¡æ. Magnetic susceptibility was measured at 5 cm intervals, using a Bartington Instruments magnetic susceptibility meter and MS2B sensor. The results show that the relationship between susceptibility values and loess-paleosol layers varies with sections. In TLD section, the maxima of magnetic susceptibility occur at L1 loess layer (with an average value 68.18 SI) not at S1 paleosol (45 SI), which is similar to that of Alaska loess, but the maxima of susceptibility in KD section is correspond with the S1 paleosol, which is similar to the loess-paleosol sequence of Chinese Loess Plateau. The differences of precipitation and altitude between the two sections are responsible for their difference of magnetic susceptibility. High altitude and relative abundant precipitation is helpful to develop soil layers. However, more factors such as tectonic, mountain shade should be considered, and also more study of rock magnetism and mineral are necessary to confirm this case.
PP23A-1069
Central Asian Glacier Sensitivity and Regional Climate: Past and Present
A surface energy- and mass-balance model that captures the interactions between glaciers and climate on regional-scales is presented. The model is applied to Central Asia because of the diverse climate regimes and unusual glacier history. It is used to understand the sensitivity of equilibrium line altitudes (ELAs) to modern interannual climate variability, and to reconcile patterns of ELA changes with climate changes during the early Holocene and Last Glacial Maximum (LGM) in Central Asia. Patterns in the present day climate give rise to patterns in the dominant ablation mechanisms at the ELA. In turn the patterns in ablation give rise to patterns in glacier sensitivity to climate changes. In particular, ELAs in melt-dominated regions are most sensitive to interannual variability in temperature. ELAs in sublimation-dominated regions are most sensitive to interannual variability in precipitation. The patterns of glacier advance and retreat during the early Holocene and LGM, in the melt-dominated regions, are both due to the patterns in temperature change. Glaciers in sublimation-dominated regions are highlighted as being acutely sensitive to even small changes in numerous atmospheric variables. For present day, Holocene, and LGM, changes in clouds are important in all regions through their influence on the shortwave and longwave radiative fluxes, which dominate the surface energy balance at the ELA. This work highlights the importance of a systematic analysis of the sensitivity of glaciers to changes in climate.
PP23A-1070
A Multi-Proxy Approach to Reconstruct the Hydrological Changes and Holocene Climate Development of Nam Co, Central Tibet
Holocene lake level fluctuations of Nam Co, Central Tibet, as an expression of monsoon strength variations are recorded in a 2.6 m long sediment core dating back at least 7.2 cal. ka BP. By means of a multi proxy approach integrating sedimentological, geochemical and mineralogical analyses with special focus on compound-specific hydrogen isotope ratios of sedimentary n-alkanes Nam Co Holocene climate evolution is divided into at least five depositional units. Additionally, geomorphological features in the catchment such as beach ridges and lake terraces point to pre-LGM high stands. Sands and sandy silts at the base of the core are interpreted as beach sediments. This suggests that lake level was about 35 m lower than today before approx. 7300 cal years BP. Sediments in unit I (until ~5.8 cal ka BP) are assumed to be deposited at highest lake levels within the sediment sequence. Isotopically depleted terrestrial and aquatic n-alkanes imply high precipitation and melt water input suggesting a positive water balance. Continuous increasing aquatic productivity points to favorable environmental conditions. Unit II (~5.8 cal ka BP to ~4.2 cal ka BP) being characterized as transition zone reflects stable hydrological conditions with the beginning of lake level decrease. Within this unit two remarkably drier periods with increased evaporation occurred around 5.75 cal ka BP and around 4.75 cal ka BP leading to significant enrichment of lake water \( δD \) values. Significant lower lake levels as consequence of a dryer climate with less monsoonal precipitation, higher evaporation rates and increased moisture recycling in the catchment are reflected in the sediments in Unit III (~4.2 cal ka BP to ~1.75 cal ka BP). Most pronounced dry periods are recorded around 3.75 cal ka BP and 2 cal ka BP again leading to deuterium enrichment of aquatic derived n-alkanes. A break of the proceeding lake shrinkage and salinisation occurs in the first section of Unit IV (~1.75 cal ka BP to ~800 cal years BP to ~500 cal years BP) where an ongoing increase in precipitation and runoff leads to at least a stable but still low lake level. The most recent Unit V (since 500 cal years BP) is characterized by an intensive progressing lake shrinking due to intensive evaporation but with intermittent monsoonal precipitation events being reflected by the variations in the geochemical parameters referring to alternating humid and arid periods at Nam Co. Although correlation with other lake records from the Tibetan Plateau suggests an overall agreement with the broader picture of Holocene environmental evolution, inconsistencies still exist concerning reliable chronologies. Thus, further research is needed to improve the spatiotemporal interpretation of hydrological variations in association with alternating monsoonal circulation across the Asian continent.
PP23A-1071
Regional Reconstruction of Fire and Climate in Western Mongolia During the Past 1000 Years: Multi-Proxy Analysis of Sediments From Nine Lakes.
Northwestern Mongolia is an arid region of great climatic transition situated at the boundary between Siberian sub-arctic habitats, and the monsoon affected deserts of the south. Mongolia is among the high-elevation mid- latitude zones affected most strongly by modern climate change, however, there are relatively few records documenting either temporal or spatial patterns in climate or fire in this region for the past 1000 years. We conducted a multi-proxy (charcoal, LOI, IRM and ARM/IRM, P, diatoms and bSi) analysis of dated (lead-210 and AMS-Carbon) short cores (1-2m) of sediment from nine lakes along an ~ 550 km E-W transect in order to establish a regional history of climate and landscape change. Charcoal and other proxies showed considerable site to site and temporal variation likely reflecting regional heterogeneity in climate, lake-specific differences in source materials and runoff and diagenesis. Charcoal influxes were generally higher during the period 1200-1600 cal yr AD than 1600-2000 cal yr AD for 5 of 9 locations suggesting a shift to drier and/or cooler conditions, a conclusion which is underscored by a roughly synchronous decrease in the flux of bSi dating to ~ 1500 cal yr AD. IRM also shifts around 1500 AD, increasing at 6 of 9 sites and dropping at the remaining three sites. Recent years have seen major change, and charcoal at 8 of 9 sites dropped to virtually zero after 1850 cal AD while IRM, sediment-P, bSi flux all rose, coincident with increases in epilimnetic phosphorus from diatom-based reconstructions. Our data suggest that increased erosion and heightened nutrient loading to the lakes during the 20{th} century may be the combined product of drought and increased grazing intensity. Marked differences in proxy responses within and among our lakes highlight the need for climate reconstructions to be based on multiple sites and multiple proxies and to account for land use in combination with abiotic climate factors when examining changes to the landscape.
PP23A-1072
Regional Reconstruction of Fire and Climate in Western Mongolia During the Past 1000 Years: Modern Lake Systems and Their Connection With Climate
The Valley of the Great Lakes in western Mongolia is a unique ecosystem comprising a wide variety of terrestrial and aquatic habitats. Little is known about the long-term history of the region or the relative impact of climate and land-use on ecosystem development. A hydrobiological survey from 2004-2005 has elucidated patterns in the distribution of aquatic biota (ostracodes, diatoms, and chironomids) as well as patterns in lake sedimentation and terrestrial inputs (based on charcoal, loss-on-ignition, and sediment magnetic properties) related to modern climate and land-use. Over 50 modern lacustrine systems were sampled, allowing for a greater understanding of modern processes in this unique system as well as offering a method for calibration and interpretation of long- term sediment records recovered from the lakes. Low concentrations of charcoal were found in only 30% of surface samples (those fringed by thick bands of Phragmites) suggesting that fire is not a common feature in the modern landscape. Across sample sites organic content of lake sediments (2-50%) decreased from east to west and the concentration and size of magnetic particles (IRM) increased, likely reflecting decreases in effective annual precipitation. Variability in the chemical and biological characteristics among sampled lakes is strongly controlled by the precipitation to evaporation balance; ionic composition varies with lake salinity and both the composition and concentration of salts are dominant factors controlling the species diversity and richness among all sampled taxonomic groups. Correspondence analysis (CCA) demonstrates that both salinity and total phosphorous concentrations account for unique and significant fractions of the observed variability in diatom communities among the lakes, allowing for the development of inference models for down-core analyses. Using these diatom-based inference models along with a modern calibration of lake sedimentation patterns, down core changes can be assessed in terms of both P-E and nutrient loading to these systems.
PP23A-1073
Atmospheric Circulation Changes During the Little Ice Age in NW China: a Late Holocene Oxygen Isotope Record From Lake Qinghai, NE Tibetan Plateau
We present a decadal-scale δ 18O record from lake sediment carbonates spanning the last 1500 years from Lake Qinghai (37°N, 100°E), a large, hydrologically closed, brackish lake on the NE Tibetan Plateau. Specifically, we focus on the Little Ice Age (LIA), which has been widely recognized as a cold period in the Northern Hemisphere between ~ AD 1550 and 1850, but it's causes, timing and climatic manifestation within the monsoon domain remain unclear. Lake Qinghai presently lies near the modern limit of the East Asian monsoon, but the Siberian High and westerly storm flow also influence it. Based on the conventional interpretation of changes in δ 18O in closed basin lakes, as a balance between precipitation and evaporation (P/E), the depletion of 18O in the δ 18O record from AD 1300 to 1825 implies an increase in precipitation during a period synonymous with the LIA, suggesting increased monsoon intensity at this time. However, we argue that this observed trend during the LIA is a result of changes in atmospheric circulation rather than monsoon strengthening. The timing of these more negative δ 18O values coincide with a period of decreases in reconstructed monsoon rainfall based on a δ 18O stalagmite record from Dongge Cave in central China, as well as occurring during a well-documented southward displacement of the inter-tropical convergence zone. Together, this suggests that the influence of the East Asian monsoon was greatly reduced. Therefore changes observed in the δ 18O record during the LIA must be controlled by other factors. Comparison of our record with variations in δ 18O from the nearby Dunde ice core demonstrate that during the LIA there were significant changes in the δ 18O of precipitation. This would have led to changes in the δ 18O of lake water, suggesting that variability in the composition of input waters (in particular precipitation) was a key control. The δ 18O of precipitation is, in turn, controlled by moisture source and air temperature, indicating changes in atmospheric circulation during the LIA is the primary cause of δ 18O variability observed in the Lake Qinghai record, with a switch to more westerly- dominated climate.
PP23A-1074
Tooth Enamel δ13C and δ18O Variations in Modern and Archaeological Horses From Northern Kazakhstan as Indicators of Regional Climate
In this study, the oxygen and carbon isotope values of tooth enamel were measured in forty-one modern and twenty-three Copper Age (3600 – 3100 B.C.) horse specimens from the grassland steppe region of northern Kazakhstan. Modern tooth enamel δ13C and δ18O values were compared with the carbon isotopic compositions of local vegetation and the δ18O values of meteoric waters. Tooth enamel isotope values within the Copper Age specimens (attributed to the so-called Botai culture) were, in turn, compared with modern samples. Average carbon isotopic values within modern bulk tooth enamel samples ranged between -13.7 and -12.0‰ (VPDB). This suggests that the diet of modern northern Kazakhstani horses is comprised almost entirely of C3 plants (considering enamel-diet fractionation factors) consistent with documented grassland compositions within the region. The observed amplitude of δ13C variations within individual teeth (typically less than ~2‰) suggests only minimal seasonal variation in the δ13C of grasses attributed to heat and water stress. Alternatively, the minimal seasonal changes observed within intra-tooth δ13C values may be the direct result of fodder provisioning. Ingested water δ18O values derived from oxygen isotope ratios within bulk tooth enamel samples appear statistically indistinguishable from estimates of regional precipitation, suggesting that Kazakhstani horse tooth enamel δ18O measurements may be used as a direct estimate of the oxygen isotopic composition of meteoric waters. Intra-tooth oxygen isotopic variations therefore reflect the pronounced seasonal variability in precipitation δ18O values tied to temperature changes and amount effects observed annually within Kazakhstan. However, these intra-tooth isotopic variations exhibit slightly reduced amplitudes relative to meteoric water values, suggesting that horses likely consume water from buffered sources such as lakes and wells. Average bulk tooth enamel δ13C values within archaeological samples (-12.1 ±0.4 ‰) were nearly identical to values measured within modern horse specimens (-11.6±0.3 ‰) suggesting that dietary patterns and feeding regimes between the Copper Age and present were relatively similar. Average ingested water δ18O values derived from oxygen isotope ratios within Copper Age bulk tooth enamel samples were, however, significantly different (reduced by nearly 3‰) from modern samples. Intra-tooth δ18O values within archaeological samples also exhibit attenuated variations, ranging only ~4‰. In contrast, intra-tooth δ18O values within modern horse specimens varied by nearly 9‰. Observed differences between average bulk tooth enamel delta18O values may reflect reduced mean annual temperatures, greater rainfall, and/or changing source water δ18O values during the Copper Age. Alternatively, waters ingested by Copper Age horses may have been less affected by evapotranspiration. The relatively low delta18O suggests that meteoric waters ingested by Copper Age horses were either less affected by evapotranspiration or the region experienced more rainfall than at present. Furthermore, the reduced amplitude of intra-tooth variations within archaeological samples suggests that seasonality was likely less pronounced during the Copper Age.
PP23A-1075
Lake Sediment Records of Late Holocene Climate Change in the Khanuy Valley, Arkhangai Aimag, North-Central Mongolia and Implications for Local Bronze and Iron Age Cultural Histories
Late Holocene geochemical records from three lakes in the Khanuy Valley, Arkhangai Aimag, north-central Mongolia document centennial and millennial-scale climate variability within central Asia. The oldest sediments of the shallow Tsegeen Nuur basin (49.09°N, 101.86°E) and nearby Sharga Nuur (48.92°N, 101.96°E) indicate lake filling and open water deposition by at least 3600 years before present (yrs. B.P.). Minimum oxygen isotope (δ18O) values, suggesting high water levels and relatively wet conditions, are preserved in biogenic carbonates (ostracod shells) from both lakes during the same time interval. Mid-core sedimentary sequences in Tsegeen Nuur and Sharga Nuur (~2200 to 400 yrs. B.P.) exhibit weak blocky and columnar structures. These lithologic changes indicate lake drying, sub-aerial exposure, and some soil development. However, these soil-like horizons contain sparse shell remains of both ostracods and bivalves and therefore suggest that both lakes held water at least periodically during this time. Ostracod shells from this interval record the greatest δ18O values and support the inference for low lake stage. No evidence exists for lake desiccation at a deeper and higher elevation lake core site (Doroo Tsagaan Nuur, 49.02°N, 101.20°E) located approximately eighty kilometers west of the Tsegeen and Sharga Nuur basins. This also suggests that although late Holocene moisture availability was significantly reduced, aridification was likely not extreme. At Tsegeen and Sharga Nuur, wet conditions appear to have returned after 400 yrs. B.P., as indicated by a decrease in δ18O values and the resumption of lacustrine deposition. It should be noted that archaeological evidence suggests that the Khanuy Valley was greatly populated between ~3200 and 2700 yrs. B.P., roughly coinciding with the wettest period recorded within these lake core sites. Human occupation of the Khanuy Valley may therefore have been linked, at least in part, to regional climate changes.
PP23A-1076
Late Holocene Climate Changes Derived From Multi-proxy Lake Sediment Records in the Northeastern Tibetan Plateau and Possible Solar Forcing
Solar variation has been recognized as an important forcing on centennial-scale climatic changes from high to low latitudes in the North Hemisphere. In eastern Asia, several records on monsoon activities and regional temperature over the last 2000 years have been correlated to solar forcing. However, in arid Northwest China, the impact of solar forcing on regional climate variations is poorly understood due to the complex topographic setting. Moreover, few lake sediment records have been recovered with adequate resolution to investigate centennial- scale regional climate changes in this period. Recently, we obtained two short cores from two, paired, hydrologically connected but contrasting fresh and saline lakes, Hurleg Lake (core HL06-2) and Toson Lake (core TL06-1) in the northeastern Tibetan Plateau. Chronology was controlled by Pb-210 and Cs-137 analysis on both cores, 5 calibrated AMS-14C dates on plant fragments in HL06-2 and inter-site correlation. Loss-on-ignition analysis results from both cores show consistent and coherent changes in carbonate content, ranging from 30- 60% in HL06-2 and 15-35% in TL06-1. In our pilot study at Hurleg Lake, surface samples along a transect of water depth show that carbonate content increases with water depth. Ostracode and mollusc abundance in both cores shows a striking reverse relationship with carbonate content: there are abundant ostracode shells at low carbonate levels. So, increased ostracode and mollusc shells may suggest littoral environment. The preliminary data from LOI and ostracode abundance indicate clear periodic variations in effective moisture with a cycle of 218 years. Also, the Artemisia/Chenopodiaceae pollen ratios from both lakes show large oscillations between xx and xxx, with similar significant centennial periodicities. These centennial-scale oscillations at these lakes show similarities with tree-ring record during the late Holocene from mountains just north of study sites. In addition, the good correlation between our records and the oxygen isotope record from Dunde ice core may represent a wet/cool and warm/dry climate association, which is in contrast to monsoon influenced region with a wet/warm and cool/dry climate association. The similar trend between the curves from both cores indicates synchronous hydrochemical responses to climate forcing in the paired contrasting lakes, but possibly with dampened amplitude in the saline lake. Our new results and future stable isotope data likely suggest a warm/dry climate association in Eurasian continental interior and possible solar forcing for the 218 year drought frequency during the last 2000 years.
PP23A-1077
Late Holocene Climatic Variability in Northern Kazakhstan: Preliminary Evidence From Lake Sediment Lithostratigraphic and Stable Isotope Analyses
In June and July 2006, eleven short (<150 centimeters) sediment cores were recovered from seven lakes within the Soltustik Qazaqstan oblast, northern Kazakhstan. To date, we have completed whole-core magnetic susceptibility measurements of the recovered sediments, as well as bulk geochemical measurements (percent organic matter, percent calcium carbonate, etc.). Basic core lithology was also determined by smear-slide mineralogy and visual inspection for Munsell color, texture and grain size, sedimentary structure, and biogenic features. Preliminary radiocarbon dates indicate recovery of high-resolution sediment records spanning the last ~2000 years. We anticipate that a future lake sediment coring campaign (with equipment designed to recover much longer cores) will permit collection of complete Holocene sections at all sites. Because of the high density of shell materials within these lakes, we also expect to generate continuous stable isotope data sets that, when coupled with sedimentological and biological analyses, will provide valuable climate information. Initial efforts have focused on sediment profiles from the Beloye basin. Evaporative loss from the lake is substantial as demonstrated by the nearly 10‰ enrichment of lake waters relative to local meteoric waters (springs, rivers, and rainfall). Temporal changes in the 18O/16O ratio of the lake waters should therefore be recorded in the oxygen isotopic composition of the abundant carbonate microfossils (ostracode and gastropod shells) preserved in the basin deposits. Preliminary oxygen isotope records from Ozero Beloye reveal δ18O values ranging from -5.9 to -3.4‰. Relatively low carbonate oxygen isotope values are documented between ~480 and 150 years before present. This period of low δ18O, roughly coincident with the Little Ice Age, may indicate greater moisture availability and/or decreased regional temperatures. Oxygen isotopic values in the Beloye sediment record were greatest prior to ~500 years before present and between 150 and 50 years before present, suggesting greater aridity and/or warmer conditions.
PP23A-1078
Preliminary Geophysical and Sedimentological Data From Peiku Co Tibet
Peiku Co (N28°46; E85°30, 4595 m a.s.l, surface area =<280km2) is located in a fault- bounded basin on the northern side of the Himalayas. The lake, which has been little explored prior to our Spring 2007 field expedition, is an excellent site for reconstructing past hydrological and monsoon variability as paleo- shorelines attest to effective-moisture-driven changes in lake level and ~70% of precipitation in the region is from the southwest Asian monsoon. In addition, the nearby Dasuopu ice core provides a record of climate variability and Indian subcontinent drought, which can be used to evaluate our Peiku Co record. We recovered over 40km of Chirp sub-bottom seismic profiles and three 4.5 meter long cores from Peiku Co. The cores were all collected from the same site in the southern basin from a water depth of approximately 40 meters. The Chirp data collected near the core site indicate that there is a least 9 meters of sediment in this part of the southern basin, which is twice the amount of sediment collected during our coring operations. A radiocarbon date from the bottom of one of the cores indicates that the core bottom (~4.5m) was deposited ~ 14,500 calendar years BP. Chirp data collected from the northern basin found the deepest water depth in the entire basin (~70m) and also sections of the northern basin containing at least 15 meters of sediment. A few strong reflectors occur throughout the lake and if our interpretation is correct these reflectors imply that the basal sediment found in the northern basin is older than the basal sediment found in the southern basin. In addition, in-filled channels and faults are found in many of the seismic profiles. Higher magnetic susceptibility values near the middle and bottom of the sediment cores suggest that there may have been more detrital input to the core site in the older part of the sediment record, possibly indicating more glacial runoff to the system. Additional analyses and radiocarbon dates will be necessary to validate this initial interpretation.
PP23A-1079
Glacial and Periglacial Geology of the Egiin Davaa Region, Hangay Nuruu, Mongolia
A wide variety of glacial and periglacial landforms exist near Egiin Davaa (pass) in the Hangay Nuruu (mountains) of west-central Mongolia. Today this area has permafrost but no permanent snowfields. Glaciers originated on the north side of the divide separating Arctic-seeking streams from interior drainage toward the Gobi. The cirque glaciers flowed northerly and westerly, becoming valley glaciers, some of which coalesced to form a piedmont glacier in the Davaatiin and Chuluut valleys. The piedmont glacier blocked the Chuluut Gol (river) to form glacial Lake Chuluut which had a minimum volume of 0.3 km3. The glacial lake likely drained in one or more jökulhlaups due to ice-dam failure. Part of the glacier complex flowed (probably during OIS2) southwest over Egiin Davaa and reached (at LGM) to within 1-2 km of moraines deposited during an earlier glaciation (possibly OIS6). Here and elsewhere the older moraines can be distinguished from younger moraines based on surface boulder frequency, boulder height, and hillslope gradient. Glaciolacustrine sediment upvalley of a recessional moraine in the valley of Botgon Gol has a calibrated radiocarbon age of 13,155 ± 70 ybp. This recessional moraine, at an elevation of 2300 m, is 16 km downvalley from the cirque headwall and 11 km upvalley from the LGM terminal moraine. From a separate valley we also obtained cosmogenic ages of two granitic boulders on a recessional moraine at an elevation of 2600m, ~11 km downvalley from the cirques; the boulders are on top of the 8-m-high scarp of the Egiin Davaa Fault (normal dip-slip) and yielded surface exposure ages of 14,709 ± 1005 and 16,537 ± 1174 ybp. This recessional moraine is 15 km upvalley from the terminal LGM ice position. Periglacial features are widespread. Most impressive are extensive cryoplanation terraces with terrace sets hundreds of meters high and individual terrace risers 13-22 m high. Scattered across the landscape are blockfields, patterned ground, and aufeis, plus generations of solifluction lobes on valley sides and palsas on valley bottoms. Peat from the permafrost table (base of the 70-cm-thick active layer) has a calibrated radiocarbon age of 5,695 ± 26 ybp.
PP23A-1080
Biological Ice Core Analysis in Russian Altai
In July 2003, a 171m long ice core was excavated from top of Belukha glacier (4,200m a. s. l.) in the Russian Altai Mountains. We examined vertical distributions of microorganisms (unicellular green algae, fungal spore, yeast) and pollens for potential use of ice core dating and reconstruction of past climate. Microorganisms have no seasonal variation in pit samples, however 5 genus of pollen (Fir, Spruce, Pine, Birch tree and Mugwort) have seasonality of each dispersed season. Therefore, this ice core can be identified past seasonal layers by pollen distribution. Pollen dating analysis of ice core estimate upper 48m ice core contain 86 years snow and ice, and this dating method well correspond to the 1963 peak in Tritium. This dating analysis is more accurate than other markers (oxygen isotope, dust, chemical concentration and melt percentage). Oxygen isotope trend from 1917 and temperature record of meteorological station near the glacier slightly increased and melt percentage have some anomalies from 1950s show recent temperature rising in this region. Otherwise, microorganisms and pollen have no trend except yeast. Vertical distribution of yeast peaks are well correspond to peaks of melt percentage show that yeast cell can grow in surface snow only in the warm period when liquid water available. In 1970s and 1980s, Nitrate increased and peaked because of anthropogenic emissions. Nitrate is major nutrient of photosynthetic microorganism, however, no clear relationship nitrate between unicellular green algae.
PP23A-1081
The Implication of Elevated Lacustrine Sediments in The Middle Reach of The Yarlung- Tsangpo and Nyang River, Tibet
The interaction mechanisms among climate, crustal uplift and related erosion processes in the orogenic belt became one of the popular topics in the past decade, especially in the collisional margin of Eurasian Plate and Indian Plate where stands the most spectacular plateau in the world in terms of elevation and geomorphology. We investigated the outcrops of lacustrine deposits in the lower terraces of the Nyang River and established the stratigraphic column for entire depositional sequence. Woods and charcoals were collected for radiocarbon dating and sands for optical stimulated luminescence (OSL). Based on our observation, the alluvial and lacustrine environments occurred alternatively and represent the evolution of a moraine-induced deposition. We identified at least two coarsening upward sequences of a delta depositional system. Typically, the distinct varve sections were overlain by interbeded sand/silt with abundant ripple cross-beds, parallel laminations, and syndepositional deformations, indicating the transition of depositional environments from pro-delta to beach ridges of the frontal delta-plain. According to the preliminary radiocarbon and OSL dates from the bottom and top of the studied profile, the scenarios of paleolakes took place no younger than very late Pleistocene. The lithology and depositional succession explicate the evolution of the delta and suggest that it has experienced episodic aggradational stages during the late Pleistocene.
PP23A-1082
Aeolian dust dynamics in Central Asia during the Pleistocene: driven by alternating atmospheric circulation patterns and/or the seasonal shift of the Asiatic polar front
Loess-palaeosol sequences preserve detailed archives of climate change, reflecting the dynamics of aeolian dust sedimentation and the palaeo-dust content of the atmosphere. The detailed investigation of particle size distributions of windblown sediments is an increasingly used approach to assess the palaeorecord of aeolian dust dynamics. The Central Asian loess belt offers the potential to carry out granulometric studies and to reconstruct Pleistocene atmospheric circulation patterns in Eurasia. In this study we present the aeolian dust record of the loess sequence at Remisowka (Almaty, SE Kazakhstan), which reflects a detailed signal of glacial-interglacial dynamics in Central Asia. Based on radiocarbon and amino acid geochronologic data, long-term semi- continuous trends in the aeolian dust record of the Last Glacial Cycle are measured in order to interpret their palaeoclimate signal. In consideration of the modern synoptical atmospheric circulation patterns and aeolian dust transport in Central Asia, it is likely that the observed trends reflect a long term signal of seasonality, triggered by changes in duration and permanency of the seasonal shift of the Asiatic polar front during the middle to late Pleistocene. Previously published models, which focused on the glacial-interglacial reciprocity of the zonal Westerlies and Asiatic high in Central Asia, were overly simplified and should be modified to include the influence of the Asiatic polar front. As the position of the high level planetary frontal zone mainly affects the development and seasonal shift of the Asiatic polar front, it is likely that an inter-hemispheric mechanism exists, that links dust deposition between Europe and Central Asia.
PP23A-1083
Satellite-based Paleo and Recent Lake Changes across the Tibetan Plateau
The Tibetan Plateau, home to the world's largest high-altitude lake group, is experiencing significant climate change with a pronounced temperature rise of 0.16oC per decade. Tibetan lakes have been impacted greatly, and in return they serve as a sensitive indicator of regional and global climate and water cycle variability. Past lake dynamics is essential for us to better understand the current and inferred future lake changes. Owing to fact that paleo lake shores have been extensively preserved on this remote plateau, paleo lake change since the late Pleistocene (about 25 ka BP) can be inferred with the assistance of digital elevation models from paleo shorelines visible on high-resolution imagery. We have recovered the lake extent more than 650 major contemporary lakes occupying a total area of 21,613 km2, and it turns out that these lakes were broken from original 173 late Pleistocene mega lakes. The total lake area shrinkage and water loss are conservatively estimated at 42,109 km2 and 2,936 km3 respectively. Nearly two-thirds of late Pleistocene lake area has disappeared. More recent lake dynamics over the past 30 years is monitored using archived satellite data, and only minor changes are found in most areas. The detected paleo and recent lake changes exhibit strong spatial patterns. Three distinct zones of paleo changes can be identified trending in the northeast to the southwest direction. Lakes in the first zone have only minor water-level drops (less than 20 meters). The second zone is the moderate zone, with 20-60 meter water level drops. Lakes in the third zone have the greatest water-level drop, up to 285 meters. Paleo shorelines are found extensively in this zone. The spatial distribution of the zones is found highly related to the Quaternary glaciation patterns. Glacial dynamics and stream network changes and other factors may explain the detected recent lake changes. It is found that glacial dynamics has the greatest impact on the detected paleo and recent lake changes, and will continue to play a critical role on Tibetan lake dynamics in the near future.
PP23A-1084
Oxygen isotope composition of modern pedogenic carbonate from the southern margin of the Tibetan Plateau
Oxygen-isotope paleoelevation estimates of large plateaus provide important geodynamic constraints on the teconic evolution of orogenic systems as well as offering insight into the dynamic feedbacks between surface uplift and regional- to global-scale climate systems. If the isotopic lapse rate (δ18O vs elevation) is known, then the oxygen isotope composition of ancient meteoric water can be used to estimate paleoelevation. The oxygen isotope composition of pedogenic carbonate preserved in paleosols has been used as a proxy for the oxygen isotope composition of soil water in order to reconstruct paleoelevation in a number of settings. Isotopic equilibrium between carbonate and water is assumed in order to calculate the δ18O value of soil water from measured δ18O values of pedogenic carbonate (δ18Opc). Uncertainties surrounding the temperature of isotopic equilibrium and the degree of evaporation of soil water limit the precision of elevation estimates from pedogenic carbonate. In this study, measurements of the oxygen isotope composition of pedogenic carbonate forming in modern soils from the Mt. Everest Region of Tibet are compared with modern meteoric water δ18O values (δ18Omw) to calibrate δ18Opc as a proxy for elevation. Pedogenic carbonate samples coating the underside of clasts were collected along depth profiles in soils at different elevations ranging from 3750 - 5200m on the southern margin of the Tibetan Plateau. Incipient soils developing in the lowest and presumably youngest river terraces were chosen for δ18Opc measurements because these are the most likely to have formed under the influence of modern precipitation. The oxygen isotope composition of modern spring and stream waters along the Bhote Kosi and Arun River were also measured in this study and agree well with previously published elevation- δ18Omw relationships for the Himalayas. Average δ18Opc values below 50 cm in the modern soils were used to calculate equilibrium δ18Omw values which were in turn used to calculate elevation from this relationship. Calculated elevations were compared with measured elevations for each location. Using estimates of mean annual temperature for isotopic equilibrium between pedogenic carbonate and soil water, the calculated elevations average ~800m higher than actual elevations. If evaporation measurably increased the δ18O value of soil water in these soils, predicted elevations would be lower, not higher, than actual elevations. It is therefore unlikely, despite the sparse vegetation cover on these terraces, that evaporation affects the oxygen isotope composition of soil water below 50 cm. This conclusion is supported by depth profiles which suggest δ18Opc does not change below ~50 cm. Overestimation of elevations is explained by pedogenic carbonate formation near maximum soil temperature, a conclusion also drawn from previous carbon and oxygen isotope studies of pedogenic carbonate. If estimates of maximum soil temperature are used to calculate ancient meteoric water δ18O values from δ18Opc in Nepalese and Tibetan paleosols, the resulting paleoelevations are at the low end of the ranges previously reported and agree with the range of modern plateau elevations.